1. Field of the Invention
The present invention relates to a fuel delivery apparatus that delivers fuel to an engine. More particularly, the present invention relates to a fuel delivery apparatus that accurately delivers fuel to a V-type engine.
2. Description of the Related Art
Return type fuel delivery apparatuses are widely used for supplying fuel in engines. This type of fuel delivery apparatus includes a pressure regulator, a delivery pipe and a return pipe. The pressure regulator, which is located at one end of the delivery pipe, controls the fuel pressure in the delivery pipe to approximate a predetermined pressure level. Surplus fuel in the pressure control operation is returned to a fuel tank via the return pipe.
To simplify the structure of the fuel delivery apparatus, returnless type fuel delivery apparatuses having no return pipe have been used. This type of fuel delivery apparatus has been classified into two groups: complete returnless type and simplified returnless type. A complete returnless type fuel delivery apparatus returns no fuel to the fuel tank. This apparatus includes a fuel pump located in the fuel tank. The pump is controlled for sending fuel from the fuel tank to the delivery pipe based on the detected pressure of the fuel in the delivery pipe. A simplified returnless type fuel delivery apparatus, on the other hand, recirculates fuel within the fuel tank. In this apparatus, a fuel pump is located in the fuel tank and connected to a delivery pipe via a fuel pipe. A pressure regulator is also located in the fuel tank and controls the pressure of the fuel sent to the fuel pipe from the fuel pump. Surplus fuel in the pressure control operation is directly returned to the fuel stored in the tank.
Complete returnless type fuel delivery apparatuses have a drawback in that it is difficult to accurately control the fuel pressure in the delivery pipe. Therefore, simplified returnless type fuel delivery apparatuses are more commonly used.
The above two types of returnless type fuel delivery apparatuses control the fuel pressure from the fuel tank within the tank, which is distant from the delivery pipe. Therefore, when fuel pressure in the delivery pipe becomes temporarily low as the injector opens, fluctuation of the fuel pressure in the delivery pipe dissipates more slowly than in return type fuel delivery apparatuses. This tendency appears especially in a simplified returnless type fuel delivery apparatuses, since fuel pressure is controlled by the pressure regulator in the fuel tank, which is distant from the delivery pipe.
The fluctuation of fuel pressure sometimes remains in the delivery pipe, depending on the engine speed, until the next time the injector is opened. In this case, such fluctuation, in synergy with another fluctuation generated by another injector's opening, generates continuous pressure fluctuation in the delivery pipe. If the frequency of this fluctuation matches the resonance frequency of the delivery pipe, resonance occurs and continues intermittently. The resonance frequency of the delivery pipe and the engine speed at which the resonance occurs tend to become lower as the delivery pipe is formed longer.
In a V-type engine shown in FIG. 9 (FIG. 9 shows the intake-manifold of a six-cylinder V type engine), the pressure fluctuation causes variation of the air-fuel ratio in a practical engine speed region. Smooth rotation of the engine is thus hindered.
The V-type engine has a pair of delivery pipes 101, 102, each of which is arranged along a bank of cylinders. A supply pipe 104 is connected to the upstream end of the first delivery pipe 101. The downstream end of the first delivery pipe 101 is connected to the upstream end of the second delivery pipe 102 by a pipe 103. In other words, the delivery pipes 101, 102 are connected in series. This elongates the fuel passage.
The relationship between the changes of fuel pressure in the delivery pipes 101, 102 and fuel injection timing will now be described with reference to FIG. 10. The upper half of FIG. 10 is a graph showing changes of the fuel pressures in the delivery pipes 101, 102. The lower half of FIG. 10 is a timing chart showing the fuel injection timing (fuel injection command signals) of first to sixth cylinders.
As shown in FIG. 10, in a fuel delivery apparatus shown in FIG. 9, fuel pressure fluctuations of the substantially identical waveforms occur at the same timing in the delivery pipes 101, 102. When fuel is injected from one of the injectors (not shown) connected to the first delivery pipe 101 into a first cylinder #1, fuel pressure fluctuation occurs not only in the first delivery pipe 101 but also in the second delivery pipe 102. This fuel pressure fluctuation remains in the second delivery pipe 102 until fuel is injected into a second cylinder #2 from an injector (not shown) connected to the pipe 102.
As the intervals between each fuel injection become shorter, the intervals between pressure fluctuation generated by the fuel injections also becomes shorter. When the frequency of the pressure fluctuation matches the resonance frequency of the delivery pipes, resonance occurs in the delivery pipes as shown in FIG. 11.
The resonance fluctuates the pressure at which fuel is injected into intake ports (not shown) from injectors. Thus, the injected amount of fuel fluctuates. The solid line in the upper half of FIG. 12 shows the oscillating waveform of the fuel pressure caused by the resonance, while the broken line shows an average fuel pressure. The lower half of FIG. 12 is a timing chart showing the fuel injection timing (fuel injection command signals).
When a valley (or a peak) of the oscillating waveform of the fuel pressure synchronizes with a fuel injection release, fuel is injected into a suction port at a pressure that is by far lower (or by far higher) than the average fuel pressure. This varies the amount of injected fuel per unit of time. Accordingly, the air-fuel ratio in the engine deviates from the air-fuel ratio computed based on the average fuel pressure. This prevents the implementation of desired engine characteristics.